docs: def get_reflectance_lut(self):
          """Read the LUT with reflectances as a function of wavelength, satellite zenith
          secant, azimuth difference angle, and sun zenith secant
  
          """
          if self._rayl is None:
              lut_vars = get_reflectance_lut(self.reflectance_lut_filename)
              self._rayl = lut_vars[0]
              self._wvl_coord = lut_vars[1]
              self._azid_coord = lut_vars[2]
              self._satz_sec_coord = lut_vars[3]
              self._sunz_sec_coord = lut_vars[4]
          return self._rayl, self._wvl_coord, self._azid_coord,\
              self._satz_sec_coord, self._sunz_sec_coord